Troubleshooting Brake Controller Installations

Even the most experienced installer will encounter it from time to time: the brake controller installation is finished, the wires have all been run, but something is going wrong. Whether your controller is showing an error message or the trailer brakes just aren't working, there are a number of troubleshooting techniques you can use to get the problem fixed and get back on the road. Using the following information and testing procedures, you should be able to pinpoint and eliminate the most common issues encountered during and after a brake controller installation.

Common Brake Control Issues

Problem

Possible Issues

Testing Procedures

Brake controller display does not show that trailer is connected.
  • Short on brake signal wire, trailer or vehicle side.
  • Corrosion in trailer and/or vehicle plug.
  • Short on brake magnets on trailer.
  • Malfunctioning brake magnet(s).
  • Method 1
  • Method 2
  • Method 3
  • Method 4
Brake controller loses connection to battery ground.
  • Ground wire was not connected to negative battery terminal, ground area does not have solid connection to ground.
  • Adapter wiring does not match OEM connector on vehicle.
  • Ground connection to negative battery terminal is loose.
  • Ground wire has been damaged and exposed wiring is touching a metal area.
  • Connect ground wire to negative battery terminal.
  • Method 1
  • Method 3
Brakes are applying too aggressively for the brake controller settings.
  • Brake assemblies are not properly adjusted.
  • Boost/Gain on brake controller is set too high for trailer size.
  • Adjust brakes properly (see video).
  • See brake control owner's manual for proper boost/gain settings for trailer size.
Trailer brakes only work with manual control, not with brake pedal. (Be sure to test for proper brake controller function with unloaded trailer in a safe area where you can reach low road speed before you determine that the brake controller is not working)
  • Incorrect stoplight wire connection.
  • Adapter wiring layout does not match OEM connector on vehicle.
  • Method 1
  • Method 2
Brake controller detects an overload condition during use.
  • Trailer has too many brakes for brake controller to handle.
  • Corrosion in trailer and/or vehicle plug.
  • Brake signal wire on trailer is damaged, exposed wiring is touching metal area or another circuit.
  • Malfunctioning brake magnet(s).
  • Check brake control owner's manual for limit on number of trailer brakes.
  • Method 1
  • Method 3
  • Method 4
Display is erratic while braking.
  • Short to battery on 12V wire connection.
  • Short on brake signal wire, trailer or vehicle side
  • Corrosion in trailer and/or vehicle plug.
  • 12V wire was not connected to vehicle battery, 12V source used is not constant.
  • Method 2
  • Method 3
  • Connect 12V wire to positive battery terminal.
Brake controller detects a short on the brake wire while vehicle is idling.
  • Corrosion in trailer and/or vehicle plug.
  • Brake signal wire on trailer or vehicle is damaged, exposed wiring is touching metal area.
  • Method 3
Trailer brakes engage when it is plugged into the vehicle.
  • Incorrect stoplight wire connection.
  • Corrosion in trailer and/or vehicle plug.
  • Adapter wiring does not match OEM connector on vehicle.
  • Method 1
  • Method 3
Brake controller does not turn on.
  • Connection to battery is not complete.
  • Vehicle is missing a fuse or relay required to power 12V power circuit.
  • Adapter wiring layout does not match OEM connector on vehicle.
  • Method 1
  • Check fuse block for missing fuse/relay. See vehicle-specific FAQ if available, or check owner's manual.

Basic Testing Procedures

Method 1: Verifying Correct Wire Connections (Hard Wire Installs)

  • Make sure that each wire is connected in the correct location. Standard wire colors are listed, but check connections by function if colors vary.
    Brake Controller Wire Colors Image
  • Verify that the white brake controller wire (ground function) is connected to the negative battery terminal.
  • Verify that the black brake controller wire (12V power function) is connected to the positive battery terminal with a 20 or 30 amp circuit breaker installed in line. For trailers with 2-4 brakes, use a 20 amp breaker and for trailers with 6-8 brakes, use a 30 amp breaker.
  • Use a 12V probe-style circuit tester to verify the stoplight wire (red) connection (Figure 1). Click here to see our circuit testers. The tester should show power when the brake pedal is pressed, and should not show power when the pedal is released.
  • If all connections are correct, proceed to Method 2.
Verifying Correct Wire Connections for Hard Wire Installs Image

Method 1: Verifying Correct Wire Connections (Plug-in Installs)

  • Use a 12V probe-style circuit tester to verify that power is present at OEM connector. You should be able to get a solid power reading on one pin/slot, a reading on a second pin/slot only when the brake pedal is pressed, and at least two other pins with no power present.
  • Verify that the pin/slot layout of the wiring adapter you are using matches the layout in the OEM connector. The two plugs should be mirror images.
  • Check the part number on the adapter and make sure it is the same as the listed fit for your vehicle.
  • If all connections are correct, proceed to Method 2.
Verifying Correct Wire Connections for Plug-In Installs Image

Method 2: Testing for the Brake Signal

  • Use a 12V probe-style circuit tester to verify that power is present on the blue wire behind the brake controller when you use the manual control (Figure 2). If no power is present, the brake controller may be malfunctioning and require replacement. See video for reference.
  • Without the trailer plugged in, use a circuit tester to verify that power is present at the vehicle 7-Way when the brake pedal is pressed or the manual control is used. The electric brake pin should be in the 5 o'clock position. If no power is present, proceed to Method 3.
  • With the trailer connected, check for power on the electric brake wire coming out of the trailer's 7-Way plug. You can repeat the test on this wire, moving further back toward the magnets each time. If power stops, look for a short or ground issue (Method 3).
Testing for Brake Signal Image

Method 3: Looking for a Short or Ground Issue

  • If controller was hard wired (controller wires were spliced - no plug used to connect to OEM brake controller wiring), verify that the white ground wire is attached to the negative battery terminal on the vehicle.
  • Check along any wiring that was run from front to back on the vehicle and look for spots that have been nicked, pinched, or rubbed and have copper wire showing through the jacketing. Wrap any damaged areas with electrical tape.
  • Inspect the trailer wiring that runs from the trailer plug, again looking for any damaged spots (Figure 3). Wrap any damaged areas with electrical tape or replace the wire section, if the damage is great enough.
  • Look inside the front and back sides of the vehicle and trailer plugs to determine if any white or green corrosion has accumulated over time. If you see any corrosion, you will need to either thoroughly clean the plug or replace it. A wire brush works best for cleaning.
  • Check the wires on the trailer brake magnets. Each magnet should have two wires: one for power, and one for ground. Make sure that the ground wire is attached to a clean metal area without any paint or corrosion. The power wire should be intact and have a solid connection to the electric brake signal wire. It does not matter which wire does what, just that one wire is powered and the other is grounded.
Looking for a Short of Ground Issue Image

Method 4: Inspecting the Brake Assemblies

Inspecting the Brake Assemblies Image

For more information, see:

Updated By: Dani S.Last Updated: 3/4/2021

Questions and Comments about this Article

Norm

we have a 2021 chevy 3500. when i hook up our 5th wheel and test the brakes before leaving the driveway. they work fine. about 1/2 mile down the road . the brake controller shows no display and the brakes don't work. display on dash says connection good no faults. any ideas.

Etrailer Expert
Reply from Jon G.

Is this an OEM brake controller? Typically when there are issues like this it's the result of a bad ground or a damaged wire/connection somewhere. This could be either on the tow vehicle or the trailer.

Dave D.

I've been troubleshooting a pulsing brake problem, my dual axle trailer has a distinct pulsing when braking around 50% or more and the frequency is not the same as the wheel rotation. Wiring is factory (12-14 gauge wiring) but there are some connections I can't get to to check, I've checked and the trailer draws a little over 12 amps while stationary at max gain and the resistance of each magnet is normal around 3 ohms. I tried brake isolation and found the pulse never really goes away, but increases as I hook more wheels up. I suspect this to be an amperage issue due to a faulty connection but wanted to get opinions on the matter. My ultimate plan is to rewire them all with 12 ga wire and eliminate the thru-axles wires. Thoughts? Thanks!

Etrailer Expert
Reply from Jon G.

That's a really good plan. The vast majority of the time when there are inconsistencies like that it's because of faulty wiring.

Steve M.

When manually pressing the brake controller switch I get full power to trailer brakes depending on how hard I press, but when using the foot pedal my controller is only showing 0 or 5, meaning I’m using mainly the truck brakes to stop the trailer. Any suggestions?

Etrailer Expert
Reply from Jon G.

Do you have your controller set to max settings, and is it a time-delayed controller or a proportional controller? If you don't have it set to max then that would explain why it isn't showing full power with your foot pedal, and then if it's proportional then you won't see much power unless your towing rig is actually moving due to the internal sensor in the controller.

Ryan

What if you have a functional brake controller that you’ve tested , and works, on other trailers, just installed new brake assemblies on both sides, adjust both assemblies properly, and can hear the brakes electronically activate when the brake pedal/manual override is being pressed, and yet there is still no braking happening on the trailer? Oh, and the brake controller settings have been set all the way up and down, and everything in between, still no change. Thoughts?

Etrailer Expert
Reply from Jon G.

To me that either sounds like you need to recheck the adjustment of the brakes (you should have a slight drag when free-spinning the tire) or you have a short somewhere that is reducing the power being sent back from your brake controller. Since the brake controller has been tested and works with other trailers the issue is definitely on the trailer side of things.

Ryan W.

What if you have power to the red stop wire when the brake pedal is not pressed and my Redarc Tow-pro elite is giving me an error of there being a short in the trailer brake wiring? It’s a new travel trailer and I have 13V all the way back until I get to the plug in 7 pin harness. Before the black box is 13v and after the box at the 7 pin female adapter is reading 6v. All camper lights work, but the error for a short in the blue wire.

Etrailer Expert
Reply from Kef G.

Have you traced all of your wires? Look for any corrosion or pinch points. If you find any, replace those wires.

Reply from Ryan W.

@KefG I didn’t see anything out of the ordinary but will pull the plug and play wires and check.

Etrailer Expert
Reply from Jon G.

@RyanW While you're checking your wires it would be a good idea to double check the connection with the red wire on your brake controller as well. This should be connected to a wire that only gets hot when the brake pedal is pressed. If the wire it's connected to right now is always hot then you'll want to connect it to a different wire.

Reply from Ryan W.

@JonG thanks for all the replies. Found a pinched wire on the emergency brake on the travel trailer.

Etrailer Expert
Reply from Jon G.

@RyanW Glad to hear it!



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